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Stage 3: Synthesis of 2-amino-4,6-difluorobenzoic acid A solution of sodium hydroxide (6.70 g, 167 mmol) and 30% hydrogen peroxide (6.7 mL) in water (60 mL) was added dropwise to a suspension of the stage 2 product (4.58 g, 25 mmol) in water (125 mL) and the reaction was carried out at 0 °C. Subsequently, the reaction mixture was stirred at room temperature for 20 hours. Upon completion of the reaction, the pH was adjusted to 3 with formic acid (~11 mL, taking care to control the rate of addition to prevent violent foaming), at which point the target compound began to precipitate. The precipitate was collected by filtration and dried in a desiccator using phosphorus pentoxide to give 3.72 g of white solid product (86% yield). The melting point of the product was 198-202 °C.

[1] Patent: US2008/293749, 2008, A1. Location in patent: Page/Page column 14
[2] Journal of Medicinal Chemistry, 2006, vol. 49, # 22, p. 6465 - 6488
[3] Organic Process Research and Development, 2010, vol. 14, # 5, p. 1078 - 1087